It is well known in the art that compatibility of metallic or inorganic fillers with organic polymers may be improved by surface treatment of the former with organosilanes or surfactants. For example, U.S. Pat. No. 4,336,284 teaches pretreating coal ash fly with organotitanates, organosilanes and the like.
U. S. Pat. No. 4,724,167 similarly teaches the art of procreating silicon with organopolysiloxanes, U.S. Pat. No. 4,369,265 concerns readily dispersible pigments coated with organo-silicone polymer.
U. S. Pat. No. 4,162,245 teaches the method of pretreating inorganic fillers with certain silanes which process advantageously reduces the viscosity of the composition on mixing with an organic polymer resin that can then be heat-cured. Four silanes were found to be useful in that process: (CH.sub.3 O).sub.3 SiCH.sub.2 CH.sub.2 Cl; (CH.sub.3 O).sub.3 SiCH.sub.2 CH.sub.2 CF.sub.3 ; (HCl) (CH.sub.3 CH.sub.2).sub.2 NCH.sub.2 CH.sub.2).sub.3 SiC.sub.18 H.sub.37 and (CH.sub.3 O).sub.3 SiCH.sub.2 CH.sub.2 OCOC(CH.sub.3).dbd.CH.sub.2. Other silanes were tried but found not useful. The silanes were used to pretreat filler materials in an acidic environment. The isolated filler material was then combined with the organic resin. The content of treated filler material in the final formulation was from 50 to 75 wt %, equivalent to a range of about 34 to about 62 volume percent.
Inspection of such earlier methods and compositions reveals significant drawbacks especially when high density metallic or ceramic parts are desired. Requirements for getting such a high density metallic or ceramic part include: (1) the presence of large amounts (greater than 63 volume percent) of metallic or inorganic filler in the molding composition, and (2) the filler being present often in finely divided state with an optimal particle size distribution. If one attempts to prepare such molding compositions with high loading of filler (greater than 63 volume percent) by using prior art methods, poor particle dispersion occurs, and it becomes difficult to achieve uniform mixing and fine powder dispersion, leading to high mixing torques, high mixing energies, long mixing times and difficult mixing operation, and may yield dry, friable, agglomerated compositions. This also precludes processability in conventional mixing and molding equipment.
Accordingly, it is a general objective of the present invention to provide novel molding compositions containing finely divided metallic or inorganic fillers in excess of 63 volume percent dispersed in organic binder matrix resins.
It is another object of the present invention to provide a method of surface treatment for such filler particles that increases their dispersibility and reduces mixing torques upon mixing with organic binder components at high concentrations.
It is yet another object of this invention to provide improved injection moldable compositions, that are capable of being processed by conventional mixing and molding equipment while employing low mixing torques and energies.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent from the following description and claims.